The present invention relates to a technique for controlling transmission of communication information such as voice or data to be transmitted to an access terminal (which will be referred to as merely AT, hereinafter) in a radio communication apparatus.
In a communication field, in these years, as broadband communication spreads, routers and so on are technically advanced, and the need for end users to want to receive a large capacity of streaming video, etc. at ATs is increased; much attention has been focused on a technique for broadcasting not only a large capacity of data or voice but also with use of communication resources less than unicast communication, that is, a multicast technique. The multicast is a technique for simultaneously transmitting a single packet or a data stream to a plurality of parties. A router provided between a server and a client acts to copy the packet or the data stream by a necessary number and to transmit the copies to a multiplicity of ATs. The unicast, on the other hand, is a technique for transmitting a plurality of packets or data streams to a plurality of parties in a 1:1 relation. When the same voice or data is transmitted to a plurality of ATs, routers, servers, etc.; the employment of the multicast enables a traffic flowing through a network to be suppressed or the load of an application server to be reduced, when compared with the unicast which requires transmission of a plurality of packets or data streams.
Even in radio communication, for the purpose of realizing efficient radio bandwidth use, a communication technique for receiving a single piece of voice or data at a plurality of ATs has been studied. Conventionally, 1:1 unicast communication wherein a physical channel is allocated to each AT to establish a 1:1 radio communication connection has been employed. By allocating specific one of the physical channels as a multicast channel, the same voice or data is transmitted to a plurality of ATs. That is, efficient radio bandwidth use can be realized by receiving a single data stream at the plurality of ATs. The radio wave reception states at ATs vary depending on the radio wave propagation environment between the AT and an access network (which will be referred to merely as AN, hereinafter).
In the unicast communication, 1:1 communication is carried out between the AT and the AN or sector. Thus, such adjustment can be possible as to increase the data transmission rate of voice or data to be transmitted when the radio wave reception state of each AT is good or to decrease the transmission rate when the wave reception state is bad. In the multicast communication, on the other hand, each AT is required to receive voice or data transmitted at a specific data transmission rate from a prescribed multicast channel. Thus, there exists an AT which cannot secure a bandwidth necessary for receiving data at the transmission rate and cannot receive the multicast data due to bad radio wave reception environment. Whether or not the AT can decode the received voice or data depends on a ratio in magnitude between actually received voice or data and noise signals. In order for an increased number of ATs to be capable of receiving voice or data multicast with a constant data transmission rate, it is required to increase the ratio in magnitude of the actual voice or data signal to the noise signal.
When code division multiple access (CDMA) is used as the radio communication technique, communication is carried out by selecting one of ANs (or sectors) which has the best radio wave state in the conventional unicast communication technique. For this reason, when radio waves transmitted from adjacent ANs or sectors not selected have the same frequency, the radio waves become all interference noise. As a method for increasing the ratio of actual voice or data to noise, there is described in 3GPP2 (3rd generation partnership project 2), C. S0054 version 0.9 a technique wherein the same voice or data signals are transmitted at the same timing from a plurality of adjacent ANs, and these voice and data signals are combined at an AT. Since the same voice or data signals are transmitted at the same timing from a plurality of adjacent ANs or sectors and the signals transmitted from the ANs or sectors are combined at an AT, the ratio of actual voice or data to noise can be made larger than that in the communication technique by selecting one of ANs (or sector) having a good radio wave environment. As a result, an increased number of ATs can receive the multicast data. The timing of transmitting voice or data from the ANs (or sectors) is included in control information and is informed from the ANs to the ATs at intervals of a constant period.